Reduced temperature dependent hysteretic comparator

ABSTRACT

This document discusses, among other things, apparatus and methods for controlling a hysteresis range of a voltage comparator. In an example, an apparatus can include an amplifier having a temperature dependency, a comparator configured to receive first and second currents and to provide an output voltage indicative of a hysteretic comparison of the first and second input voltages, wherein a range of hysteresis of the apparatus is controlled over a range of temperatures. In an example, the amplifier can be configured to receive first and second input voltages and to provide the first and second currents.

CLAIM OF PRIORITY

This patent application claims the benefit of priority, under 35 U.S.C.Section 119(e), to Daigle et al., U.S. Provisional Patent ApplicationSer. No. 61/416,121, entitled “VOLTAGE REFERENCE COMPARATOR WITHTEMPERATURE INDEPENDENT HYSTERESIS,” filed on Nov. 22, 2010, which ishereby incorporated by reference herein in its entirety.

BACKGROUND

Electric devices can be subjected to a wide variety of environmentsincluding a wide variety of temperatures that can change drasticallyover a relatively short period of time, such as when entering or leavinga warm building in the winter. Temperature dependencies of variouselectronic components of the electronic devices, such as voltagecomparators used to detect various events associated with the electronicdevices, can limit the performance of the electronic devices oraccessories associated with the electronic devices.

OVERVIEW

This document discusses, among other things, apparatus and methods forcontrolling a hysteresis range of a voltage comparator over a range oftemperatures. In an example, an apparatus can include an amplifierhaving a temperature dependency, a comparator configured to receivefirst and second currents and to provide an output voltage indicative ofa hysteretic comparison of first and second input voltages, wherein arange of hysteresis of the apparatus is controlled over a range oftemperatures. In an example, the amplifier can be configured to receivethe first and second input voltages and to provide the first and secondcurrents.

This section is intended to provide an overview of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 illustrates generally a block diagram example of a comparatorwith temperature independent hysteresis.

FIG. 2 illustrates generally an example comparator circuit withtemperature independent hysteresis.

FIG. 3 illustrates generally an example temperature compensationcomponent.

DETAILED DESCRIPTION

The present inventors have recognized, among other things, a circuit,such as a voltage comparator circuit, configured to provide a controlledhysteresis range at an output over a range of temperatures. In certainexamples, the controlled hysteresis range does not vary withtemperature. In an example, the circuit can be configured to receivevoltage inputs at or up to an upper rail voltage and at or down to alower rail voltage. In an example, the circuit does not require the useof a second reference voltage, such as a band gap voltage reference, toprovide hysteresis including providing a hysteresis range that issubstantially independent of temperature. Thus, the circuit can provideimproved hysteretic voltage comparison information over a widetemperature range without increasing die size or using additional powerassociated with a second voltage reference, such as a voltage referenceto provide a second hysteretic voltage threshold. In an example, thecircuit can provide an improved common mode range such that the commonmode range can operate from rail to rail minus one (V_(th)+V_(ds)).

In an example, the circuit can include a differential input pair in afolded cascode amplifier configuration with a positive feedback latching(e.g. hysteresis) circuit. In an example, the folded cascode amplifierconfiguration can allow for functionality with common mode inputs at ordose to a rail voltage. In certain examples, the circuit can include atemperature compensation component to control a range of the hysteresisof the circuit over a range of temperatures. In an example, the range ofhysteresis of the circuit, for a given differential input voltage, canvary less than about 0.01 volts over a temperature range of about 125degrees Celsius (e.g., from about −40 degrees Celsius to about 85degrees Celsius).

The circuit can be used in a variety of electronic devices includingpersonal mobile electronic devices susceptible to relatively quicklychanging temperatures. In certain examples, the circuit can providerobust performance to detect various signal changes of a mobileelectronic device, for example, signal changes associated with userinterface actions or signal changes associated with accessory devices orsensor devices.

FIG. 1 illustrates generally a block diagram of an example hystereticvoltage comparator circuit 100. In certain examples, the hystereticvoltage comparator circuit 100 can include a transconductance amplifier101, a hysteretic current comparator 102, and a temperature compensationcomponent 103. In an example, the transconductance amplifier 101 cancompare an input voltage V_(A) to a reference voltage V_(B) and providea differential current output I_(A), I_(B) indicative of the value ofinput voltage V_(A) with respect to the reference voltage V_(B). In anexample, the transconductance amplifier 101 can receive a differentialvoltage V_(A)−V_(B), and can provide a differential current outputI_(A), I_(B) indicative of a magnitude of the differential voltageV_(A)−V_(B). The hysteretic current comparator 102 can receive thedifferential current output of the transconductance amplifier 101, andcan provide a discrete output indicative of the magnitude of thedifferential voltage V_(A)−V_(B). In certain examples, the output of thehysteretic converter can transition from a first state to a second stateas the difference between the input voltages increases through a firstthreshold, and can transition from the second state as the differencebetween the input voltages decreases through a second threshold. Incertain examples the first threshold includes a higher value than thesecond threshold.

In an example, the transconductance amplifier 101 can include atemperature compensation component 103. The temperature compensationcomponent 103 can provide a bias to the transconductance amplifier 101,such that for given input voltage difference V_(A)−V_(B) thecorresponding output currents I_(A), I_(B) can remain substantiallyunchanged over a wide range of temperature. In an example, a temperaturecoefficient associated with the temperature compensation component 103can be selected to track, in an opposite manner, a temperaturedependency of the transconductance amplifier 101 as the temperature ofthe circuit varies. Such a temperature coefficient can at leastpartially reduce the magnitude of the overall temperature coefficient ofthe transconductance amplifier 101 and thus, reduce the temperaturedependency of the hysteretic voltage comparator circuit 100.

In certain examples, an integrated circuit can include thetransconductance amplifier 101 and the hysteretic current comparator102. In an example, an integrated circuit can include thetransconductance amplifier 101, the hysteretic current comparator 102,and the temperature compensation component 103.

FIG. 2 illustrates generally an example of a hysteretic voltagecomparator circuit 200. In certain examples, the hysteretic voltagecomparator circuit 200 can include a transconductance amplifier 201,such as a folded cascade transconductance amplifier, and a hystereticcurrent comparator circuit 202. In an example, the transconductanceamplifier 201 can include a current source including a resistor 206 anda plurality of transistors (e.g., M1, M2, M3, M6, M7, M8, M9, and M10,etc.). The transconductance amplifier 201 can provide current summingjunctions A, B to provide a differential current output I_(A), I_(B) tothe hysteretic current comparator circuit 202 in response to adifferential voltage IN_(A), IN_(B) received at the inputs of thetransconductance amplifier 201. Current summing can allow currentsI_(1,2) and I_(3,4) to be set independently to provide temperatureindependent hysteresis. In an example, transistors M2 and M3 can have amultiplier J larger than M1, and thus, currents I₃ and I₄ can be J timeslarger than a bias current, such as a second bias current iBias2illustrated in FIG. 2. Transistors M13 and M14 of the hysteretic currentcomparator circuit 202 can have a multiplication factor X over that ofcorresponding transistors M12 and M15. In an example, selection of themultiplication factor X can assist in establishing an upper thresholdand a lower threshold of the hysteretic current comparator circuit 202.For example, at a threshold of toggle of the hysteretic voltagecomparator circuit 200, the hysteresis amount can be given by:

${I_{A,B} = \frac{x\left( {I_{A} + I_{B}} \right)}{x + 1}},{I_{B,A} = \frac{\left( {I_{A} + I_{B}} \right)}{x + 1}},{{\Delta\; I_{A,B}} = {{{I_{A} - I_{B}}} = \frac{\left( {x - 1} \right)\left( {I_{A} + I_{B}} \right)}{\left( {x + 1} \right)}}},{{\Delta\; I_{A,B}} = {\Delta\; I_{1,2}}},{{\Delta\; I_{B,A}} = {\Delta\;{{Vin} \cdot g_{m_{9,10}}}}},{{\Delta\;{Vin}} = \frac{V_{HYST}}{2}},{{\Delta\;{Vin}} = {{{IN}_{A} - {IN}_{B}}}},{V_{HYST} = {{2 \cdot \Delta}\;{Vin}}},{V_{HYST} = {\frac{2\left( {x - 1} \right)\left( {I_{A} + I_{B}} \right)}{\left( {x + 1} \right)g_{m_{9,10}}}.}}$For temperature independent hysteresis:δV_(HYST) /δT=0.For the example voltage comparator circuit 200,

${x = \frac{M_{13,14}}{M_{12,15}}},$and I_(A)=(I₃−I₁) and I_(B)=(I₄−I₂). Thus,

$\frac{\delta\; V_{HYST}}{\delta\; T} = {{{{Const} \cdot \frac{\delta}{\delta\; T}}\left( \frac{I_{A} - I_{B}}{g_{m_{{9,10}\;}}} \right)} = 0.}$This can be achieved in several ways, for example,

$\frac{\delta\left( {I_{A} + I_{B}} \right)}{\delta\; T}\mspace{14mu}{and}\mspace{14mu}\frac{\delta\; m_{g_{9,10}}}{\delta\; T}$each can be set equal to zero. Alternatively,

$\frac{\delta\left( {I_{A} + I_{B}} \right)}{{\delta g}_{m_{9,10}}}$can be set equal to

$\frac{\left( {I_{A} + I_{B}} \right)}{g_{m_{9,10}\;}}.$

Constant hysteresis can be achieved by keeping all components of thehysteresis equation constant. For example,

${V_{HYST} = \frac{2\left( {x - 1} \right)\left( {I_{A} + I_{B}} \right)}{\left( {x + 1} \right)g_{m_{9,10}}}},{where}$${\frac{\delta\left( {I_{A} + I_{B}} \right)}{\delta\; T} = 0},{and}$$\frac{{\delta g}_{m_{9,10}}}{\delta\; T} = 0.$Generally,

${g_{m} = \sqrt{2{\mu(T)}C_{ox}\;\frac{W}{L}I_{D}}},$where

μ=mobility of the carrier,

W=channel width,

L=channel length,

$C_{OX} = \frac{ɛ_{ox}}{t_{{ox}\;}}$and is a constant where ε_(ox) can equal permittivity of a silicon oxideof the transistor and t_(ox) can equal thickness of an oxide layer ofthe transistor, and

T=temperature.

A temperature coefficient tc1 based on a first bias current source 204configured to provide a first bias current iBias1 can be created that isequal and opposite to the natural temperature coefficient of g_(m)_(9,10) . This can ensure a constant g_(m) _(9,10) over a range oftemperature variation. In an example,2I _(D) =iBias1(1+tc1(T−25)), where

T=temperature.

Therefore, in an example circuit, a temperature compensation componentcan include a first bias current source 204 configured with thetemperature coefficient tc1 to compensate for at least a portion of thetemperature dependency of the transconductance of transistors M9 andM10. Providing a first bias current source 204 to compensate for atemperature dependency of the transconductance of transistors M9 and M10can ensure that the difference between currents I₁ and I₂ issubstantially constant over a wide temperature range. However, incertain examples, the temperature coefficient tc1 of the first biascurrent source 204 can become dominant such that the sum of currents I₁and I₂ can vary over the desired temperature range. In certain examples,the temperature dependence of the first bias current source 204 cancontribute to a temperature dependence of I_(A) and I_(B).

In an example, a temperature coefficient tc2 based on a second biascurrent source 205 configured to provide a second bias current iBias2can be created. The temperature coefficient tc2 can be based on, forexample, one or more of the following:

-   -   (1) The second bias current source 205 can have a multiplier of        J through sizing of M2, M3 to M1 of FIG. 2.    -   (2) The second bias current iBias2 of the second bias current        source 205 at room temperature can be 1/K times the first bias        current iBias1 of the first bias current source 204 at room        temperature.    -   (3) A temperature coefficient tc2 of the second bias current        source 205 can be 1/L times the temperature coefficient tc1 of        the first bias current source 204.    -   (4) J, K, and L can satisfy the equation J=KL/2.        At common mode, the first order temperature coefficient can be        canceled using the following equations:

${I_{A} = {I_{B} = {{{J \cdot {iBias}}\; 2\left( {1 + {{tc}\; 2\left( {T - T_{nom}} \right)}} \right)} - {\frac{1}{2}{iBias}\; 1\left( {1 + {{tc}\; 2\left( {T - T_{nom}} \right)}} \right)}}}},\mspace{20mu}{{{ibias}\; 1} = {{K \cdot {iBias}}\; 2}},\mspace{20mu}{{{tc}\; 1} = {{L \cdot {tc}}\; 2}},{I_{A} = {I_{B} = {{{J \cdot {iBias}}\; 2\left( {1 + {{tc}\; 2\left( {T - T_{nom}} \right)}} \right)} - {\frac{K}{2}{iBias}\; 2\left( {1 + {{L \cdot {tc}}\; 2\left( {T - T_{nom}} \right)}} \right)}}}},{I_{A} = {I_{B} = {\left( {{J \cdot {iBias}}\; 2} \right) + \left( {{J \cdot {iBias}}\;{2 \cdot {tc}}\; 2\left( {1 - T_{nom}} \right)} \right) - \left( {\frac{K}{2}{iBias}\; 2} \right) - {\left( {\frac{K \cdot L}{2}{iBias}\;{2 \cdot {tc}}\; 2\left( {T - T_{nom}} \right)} \right).}}}}$From above,

${J = \frac{KL}{2}},$thereof,

$I_{A} = {I_{B} = {\left( {J - \frac{K}{2}} \right){iBias}\; 2.}}$Accordingly, currents I_(A) and I_(B) are not dependent on temperature,T.

FIG. 3 illustrates generally an example of a temperature compensationcomponent 303 including a self-biased reference 310 and one or moreoutput mirror transistors 311, 312. In an example, the temperaturecompensation component 303 can include an output mirror transistor 311that can form a portion of a first bias current source 304 to provide atemperature coefficient configured to at least partially compensate fora temperature dependence of a transconductance amplifier. In an example,the temperature compensation component 303 can include an output mirrortransistor 312 that can form a portion of a second bias current source305 to provide a temperature coefficient configured to compensate for atleast a portion of a temperature dependence of the transconductanceamplifier using the first bias current source 304. In certain examples,the temperature compensation component 303 can include the first biascurrent source and the second bias current source. In an example, thefirst bias current source 304 can be separate from the second biascurrent source 305.

In an example, the first bias current source 304 can include aresistance 320. The resistance 320 can be selected to have a temperaturecoefficient tc1 that can at least partially compensate for an overallmagnitude of a temperature dependence of the transconductance amplifierof FIG. 2. In certain examples, the resistance 320 can include more thanone resistor to allow fine tuning of the temperature coefficient tc1 ofthe first bias current source 304.

In an example, the second current bias source 305 can include aresistance 321. The resistance 321 of the second bias current source 305can be selected to have a temperature coefficient tc2 that can at leastpartially compensate for an overall magnitude of a temperaturedependence of the transconductance amplifier of FIG. 2. In certainexamples, the resistance 321 can include more than one resistor. Incertain examples, the resistance 320, 321 of the first or second biascurrent sources 304, 305 can include a semiconductor resistor, such as adiffused resistor or a polysilicon resistor.

Additional Notes

In Example 1, an apparatus can include an amplifier having a temperaturedependency, the amplifier configured to receive first and second inputvoltages and to provide first and second currents, a comparatorconfigured to receive the first and second currents and to provide anoutput voltage indicative of a hysteretic comparison of the first andsecond input voltages, and wherein a range of hysteresis of theapparatus is controlled over a range of temperatures.

In Example 2, the apparatus of Example 1 optionally includes atemperature compensation component configured to compensate for at leasta portion of the temperature dependency of the amplifier and to controlthe range of hysteresis over range of temperatures.

In Example 3, the amplifier of any one or more of Examples 1-2optionally includes first and second input transistors having atransconductance with a first temperature coefficient, wherein thetemperature compensation component of any one or more of Examples 1-2optionally includes a first bias current source having a secondtemperature coefficient, wherein the second temperature coefficient isconfigured to at least partially compensate for the first temperaturecoefficient.

In Example 4, the first bias current source of any one or more ofExamples 1-3 is optionally configured to bias the first and second inputtransistors.

In Example 5, the amplifier of any one or more of Examples 1-4optionally includes a second bias current source configured to at leastpartially compensate for the temperature dependency of the first biascurrent source.

In Example 6, the second current bias source of any one or more ofExamples 1-5 optionally includes a first current mirror, the firstcurrent mirror including a first sense transistor, a first mirrortransistor and first and second resistors coupled to the first mirrortransistor.

In Example 7, the first and second resistors of the second current biassource of any one or more of Examples 1-6 optionally include first andsecond resistor temperature coefficients to at least partiallycompensate for the temperature dependency of the amplifier.

In Example 8, the first current bias source of any one or more ofExamples 1-7 optionally includes a second current mirror, the secondcurrent mirror including a second sense transistor, a second mirrortransistor and third and fourth resistors coupled to the second mirrortransistor.

In Example 9, the third and fourth resistors of the second current biassource of any one or more of Examples 1-8 optionally include third andfourth resistor temperature coefficients configured to at leastpartially compensate for the first temperature coefficient.

In Example 10, the first sense transistor and the second sensetransistor of any one or more of Examples 1-9 are optionally a singlesense transistor.

In Example 11, the first current bias source of any one or more ofExamples 1-10 optionally includes a current mirror, the current mirrorincluding a sense transistor, a mirror transistor and first and secondresistors coupled to the mirror transistor.

In Example 12, the first and second resistors of the first current biassource of any one or more of Examples 1-11 optionally include first andsecond resistor temperature coefficients configured to at leastpartially compensate for the first temperature coefficient.

In Example 13, the amplifier of any one or more of Examples 1-12optionally includes a current mirror and first and second inputtransistors, wherein the current mirror is configured to provide currentto the first and second input transistors.

In Example 14, the amplifier of any one or more of Examples 1-13optionally includes a cascode amplifier.

In Example 15, the amplifier of any one or more of Examples 1-14optionally includes a folded cascode amplifier.

In Example 16, the amplifier of any one or more of Examples 1-2optionally includes a differential folded cascode amplifier.

In Example 17, a method of any one or more of Examples 1-16 can includereceiving first and second input voltages at an amplifier, providingfirst and second currents using the first and second voltages and theamplifier, comparing the first and second currents using a hystereticcomparator, providing an output voltage indicative of a hystereticcomparison of the first and second input voltages using the comparisonof the first and second currents, and controlling a range of hysteresisof hysteretic comparison over a range of temperatures.

In Example 18 the controlling the range of hysteresis of any one or moreof Examples 1-17 optionally includes biasing first and second inputtransistors of the amplifier using a first current source configured toat least partially compensate for first temperature coefficient of atransconductance of the first and second input transistors.

In Example 19, the controlling the range of hysteresis of any one ormore of Examples 1-18 optionally includes biasing a current mirror ofthe amplifier using a second current source configured to at leastpartially compensate for a temperature dependency of the current mirror.

In Example 20, the receiving the first and second voltages of any one ormore of Examples 1-19 optionally includes receiving the first and secondvoltages at a differential folded cascode amplifier, and the providingfirst and second currents of any one or more of Examples 1-19 optionallyincludes providing first and second currents using the first and secondvoltages and the differential folded cascode amplifier.

Example 21 can include, or can optionally be combined with any portionor combination of any portions of any one or more of Examples 1-20 toinclude, subject matter that can include means for performing any one ormore of the functions of Examples 1-20, or a machine-readable mediumincluding instructions that, when performed by a machine, cause themachine to perform any one or more of the functions of Examples 1-20.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” in thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and notrestrictive. In other examples, the above-described examples (or one ormore aspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. An apparatus comprising: an amplifier having atemperature dependency, the amplifier configured to receive first andsecond input voltages and to provide first and second currents; acomparator configured to receive the first and second currents and toprovide an output voltage indicative of a hysteretic comparison of thefirst and second input voltages; a temperature compensation componentconfigured to reduce the temperature dependency of the amplifier over arange of temperatures and to reduce a temperature dependency of a rangeof hysteresis over the range of temperatures; and wherein the amplifierincludes a cascode amplifier.
 2. The apparatus of claim 1, wherein theamplifier includes first and second input transistors having atransconductance with a first temperature coefficient; wherein thetemperature compensation component includes a first bias current sourcehaving a second temperature coefficient; and wherein the secondtemperature coefficient is configured to at least partially compensatefor the first temperature coefficient and to reduce the temperaturedependency of the amplifier.
 3. The apparatus of claim 2, wherein thefirst bias current source is configured to bias the first and secondinput transistors.
 4. The apparatus of claim 2, wherein the amplifierincludes a second bias current source configured to at least partiallycompensate for the temperature dependency of the first bias currentsource.
 5. The apparatus of claim 4, wherein the second bias currentsource includes a first current mirror, the first current mirrorincluding a first sense transistor, a first mirror transistor and firstand second resistors coupled to the first mirror transistor.
 6. Theapparatus of claim 5, wherein the first and second resistors of thesecond bias current source include first and second resistor temperaturecoefficients to at least partially compensate for the temperaturedependency of the amplifier.
 7. The apparatus of claim 6, wherein thefirst bias current source includes a second current mirror, the secondcurrent mirror including a second sense transistor, a second mirrortransistor and third and fourth resistors coupled to the second mirrortransistor.
 8. The apparatus of claim 7, wherein the third and fourthresistors of the second bias current source include third and fourthresistor temperature coefficients configured to at least partiallycompensate for the first temperature coefficient.
 9. The apparatus ofclaim 7, wherein the first sense transistor and the second sensetransistor are a single sense transistor.
 10. The apparatus of claim 2,wherein the first bias current source includes a current mirror, thecurrent mirror including a sense transistor, a mirror transistor andfirst and second resistors coupled to the mirror transistor.
 11. Theapparatus of claim 10, wherein the first and second resistors of thefirst bias current source include first and second resistor temperaturecoefficients configured to at least partially compensate for the firsttemperature coefficient.
 12. The apparatus of claim 1, wherein theamplifier includes a current mirror and first and second inputtransistors, wherein the current mirror is configured to provide currentto the first and second input transistors.
 13. The apparatus of claim 1,wherein the amplifier includes a folded cascode amplifier.
 14. Theapparatus of claim 1, wherein the amplifier includes a differentialfolded cascode amplifier.
 15. A method comprising: receiving first andsecond input voltages at an amplifier; providing first and secondcurrents using the first and second voltages and the amplifier;comparing the first and second currents using a hysteretic comparator;providing an output voltage indicative of a hysteretic comparison of thefirst and second input voltages using the comparison of the first andsecond currents; controlling a range of hysteresis of hystereticcomparison over a range of temperatures, wherein the controlling therange of hysteresis includes biasing first and second input transistorsof the amplifier using a first current source configured to reduce atemperature dependency of the first and second input transistors and toat least partially compensate for a first temperature coefficient of atransconductance of the first and second input transistors; wherein thereceiving the first and second voltages includes receiving the first andsecond voltages at a differential folded cascode amplifier; and whereinthe providing first and second currents includes providing first andsecond currents using the first and second voltages and the differentialfolded cascode amplifier.
 16. The method of claim 15, wherein thecontrolling the range of hysteresis includes biasing a current mirror ofthe amplifier using a second current source configured to reduce atemperature dependency of the current mirror.
 17. The apparatus of claim1, wherein a temperature dependence of the range of hysteresis is about0.01 volts and the range of temperature is about 125 degrees Celsius.18. The method of claim 15, wherein the controlling a range ofhysteresis of hysteretic comparison over a range of temperatures,includes controlling the range of hysteresis to within about 0.01 voltsover a range of temperatures of about 125 degrees Celsius.